1. Field of the Invention:
The present invention relates to transparent amorphous polyamides, and, more especially, to transparent amorphous polyamides produced from terephthalic acid, 2-methylpentamethylenediamine and a hindered aromatic diamine.
2. Description of the Prior Art:
Polyamides produced from aliphatic amines and from aromatic dicarboxylic acids have long been known to this art. Many polyamides are crystallized (and thus are designated "semicrystalline" polymers) and the crystallized polymers cannot be used in all fields, in particular for those applications which require transparency. Exemplary crystallized polyamides are notably those polymers produced from terephthalic acid and hexamethylenediamine, or those produced from terephthalic acid and 2-methylpentamethylenediamine (JA-A-69/019,551). Other polyamides are amorphous. They soften at a relatively low temperature and exhibit a low glass transition temperature (Tg). Exemplary amorphous polyamides include, for example, those polymers produced from terephthalic acid, isophthalic acid (70 to 85 mol % in the mixture of diacids) and hexamethylenediamine (U.S. Pat. No. 3,382,216), which have a Tg of from 100.degree. to 120.degree. C.
Amorphous polyamides are especially suitable for the manufacture of sheets, tapes, plaques, tubes, cable sheating and injection-molded shaped articles. However, because of their low Tg, these polyamides can be used only at low temperatures, and this greatly restricts their potential applications. Polyamides of higher Tg are described in French Patent FR-A-2,325,673; they are produced from terephthalic acid, isophthalic acid (15 to 30 mol % in the mixture of diacids) and 2-methyl-1,5-pentamethylenediamine, but the highest available Tg with these polyamides is 142.degree. C.
Since the Tg is an important factor that will determine the thermomechanical stability of the amorphous polymers, serious need continues to exist in this art for amorphous polyamides having a Tg higher than 142.degree. C.